1. Field of the Invention
This invention discloses an acqueous solution of a silicone containing polyelectrolyte suitable for use as a one-component coating, methods for its preparation and application in pressure-sensitive adhesive coated products, such as tapes and labels.
2. Description of the Prior Art
Pressure-sensitive adhesive tapes are generally manufactured and sold with the tape wound upon itself in convolutions to form a roll of some suitable length of tape. Consequently, when it is necessary to use the tape, it must be possible to unwind the desired length from the roll without excessive force or delamination of the backing, offsetting of the adhesive, or the like, regardless of the time or conditions under which the tape has remained in roll form prior to use. For these reasons, a coating known as a release coat or backsize is generally provided on the back side of the tape backing member, i.e., the side opposite that on which the adhesive mass is applied. Such a coat, compared to an uncoated backing member, as is its objective, offers relatively low adhesion to the adhesive mass.
Although various release agents and compositions thereof have been developed over the years, none of them, to my knowledge, accomplish all the objects desired by their use. With some release agents, the release characteristics diminish with time, and particularly at high temperatures, because of some chemical or physical change in the release material per se. Others interact with the adhesive mass so that adhesion to various substrates to which the tape is applied is adversely affected.
Whether a material will be suitable or not as a release agent, in particular for pressure-sensitive adhesive tapes, depends upon a number of factors. The lower the interfacial tension between the adhesive mass and the material used as a release coating, naturally the better release provided. However, low interfacial tension alone is not enough. The material, to be useful as a release coat, should also be of a suitable cohesive strength and possess good adhesion with the backing member.
In the 1970's, silicone emulsions in water were introduced. Generically, they were dimethylsiloxane oligomers with Si-H reactive groups. They had to be mixed with a catalyst prior to application to paper or plastic film, which made them inconvenient 2-component systems. Upon evaporation of water, a surface film of the oligomer was deposited, which built up in molecular weight, crosslinked, and a solid coating resulted. This process, called "cure", needed either high temperatures or long time at moderate temperatures.
The necessity for curing the polymeric material after deposition has placed certain restrictions on the use of silicones. This is because the temperature needed for curing, at least to the extent desired, has often exceeded the temperature which a substrate on which a release coating is deposited could withstand. This has been particularly true where the substrate is thermoplastic film or a paper-thermoplastic film laminate, care being needed to avoid melting or distorting the thermoplastic film. In paper substrates, high temperatures results in overdrying of paper.
A further disadvantage associated with silicone release polymers is their relatively poor adhesion to certain plastic films on which they are coated. This poor adhesion is thought to be due to the scarcity of polar groups in the silicone. Consequently, the use of a primer is often needed to obtain better anchorage of the silicone film to the substrate. In addition the release characteristic in itself is sometimes a problem in that too good a release is provided. Thus, they may be too easy unwind in tape rolls and, in some cases, the adhesion between the adhesive mass and release coat may be so low that the roll doesn't remain tightly wound.
All the prior art known to me discloses either 2-component silicones requiring high temperatures for curing and urethane-siloxane copolymers that can be dissolved in solvents to be suitable as coatings. None discloses a one-component siloxane polyelectrolyte that can be made in and applied from an acqueous solution.